(a) Field of the Invention
The present invention relates to a differential voltage controlled oscillator. More specifically, the present invention relates to a differential voltage controlled oscillator using cross-coupled complementary transistors, and a transceiver using the same.
(b) Description of the Related Art
FIG. 1 shows a conventional differential voltage controlled oscillator (VCO) including NMOS transistors M1 and M2, varactors Cv1 and Cv2, inductors L1 and L2, and a current source ISS.
The NMOS transistors M1 and M2 are cross-coupled, the inductors L1 and L2 and the varactors Cv1 and Cv2 form a resonance circuit, one electrode of each of the varactors Cv1 and Cv2 are coupled to each other, and a control voltage of Vc is applied to a node of each electrode thereof.
The differential conventional VCO cross-couples the NMOS transistors M1 and M2 to generate negative resistance, and uses the control voltage of Vc to control the capacitance of the varactors Cv1 and Cv2, thereby controlling the frequency of output signals.
However, it is required for the current source Iss to supply a current, corresponding to the sum of drain currents ID1 and ID2 needed for operating the NMOS transistors M1 and M2, so as to respectively supply the current to the NMOS transistors M1 and M2. Therefore, the current used by the VCO is increased and the power consumption is increased.
In addition, low-frequency noise generated by the NMOS transistors M1 and M2 and an active element (not illustrated) of the current source Iss is transitioned to an oscillation frequency of the resonance circuit, and a phase noise response of the output signals Vout+ and Vout− is accordingly degraded.
Further, the common source node of NMOS transistors provides mechanism for the flicker noise of transistor to be transferred to the oscillation frequency.